Method of making ferro-alloys



March 10, 1942. J. c. VIGNOS METHOD OF MAKING FERRO-ALLQYS Filed Jan. 23, 19511 PERCENTAGE SILICON.

INVENTOR. W

ATTORNEYG.

Patented Mar. 10, 1942 METHOD or MAKING FERRO-ALLOYS James C. Vignos, Canton, Ohio, assignor to Ohio Ferro-Alloys Corporation, Philo, Ohio, a. corporation of Ohio Application January 23, 1941, Serial No. 375,593 14 Claims, (01. 7556) This invention relates to methods of making silicon-containing ferro-alloys of carbide-forming metals such, for exampie, as chromium and manganese, and particularly to those for use in producing low carbon ferrous base alloys of. such metals, especially. stainless irons and steels.

The word ferro-alloys is used by metallurgists to designate alloys of iron with such large contents of one or more alloying elements, other than carbon, that they are used for introducing those elements in the production of alloy irons and steels. This term and the alloyscomprehended by it are well understood in the art.

The invention is desirably applicableto the production of ferro-alloys of low carbon content, and may therefore be described with particular reference thereto.- For the production of certain ferrous base alloys the carbon content of the ferro-alloys used is highly important. For instance, it is well recognized that in the production of various ferrous base alloys containing chromium, and particularly in the production of stainless irons and steels, it is essential that the ferrochrome used be of extremely low carbon content. Such ferro-alloys may therefore be referred to herein as exemplifying, but not limiting, the ferro-alloys of the carbide-forming elements with which the invention is concerned.

In the production of stainless irons and steels, I

for example, thecommon practice is to react a ferro-alloy of silicon and chromium, i. e., ferrochrome-silicon, with chrome ore to produce the desired final alloy. The carbon content of the final alloy is definitely a function of that of the ferro-alloy used, and where the carbon of the product is'important there are used ferro-alloys of exceedingly low carbon content.

application filed by me, refers to the use of a ferrochrome-silicon alloy containing 46 per cent of chromium, 35.64 per-cent of silicon, and but 0.32 per cent of carbon. Generally speaking, the

- of silicon, and 'only 0.05 per cent of carbon, while that patentee in his companion Patent No.

2,176,687 discloses the use of a similar alloy con-. taining 50 per cent of silicon, 23.4 per cent of chromium, and 0.04 per cent of carbon. 1

Because no other practical way of making such ferro-alloys with such low content of carbon has been known, most of the ferrochrome-silicon alloys used for these purposes have been produced by direct reduction of ore. In the case of termchrome this is done by reducing a charge of quartz and chrome ore with carbon, for example For example, U. S. Patent No. 1,925,886. issued on an as disclosedin Patent No. 891,898 to F. M.

Becket..

The belief in the art has been that the carbon content of all ferrochrome-silicon alloys is a function of the silicon content, the carbon being lowered, at least up to a certain point, as the silicon content is increased. This relationship is described in U. S. Patent No. 1,567,898 to F. M. Becket, and the accompanying drawing is a reproduction of the graphgiven in that patent, as representing the carbon-silicon relationship. As appears therefrom, and as described in the specification of the patent, in ferrochromesilicon alloys the carbon content of the alloy' decreases rapidly as the silicon content increases from about 17 to about40-per cent, while further increase in the silicon content up to about 67 per cent results in little or no further decrease in the carbon content. According to the patent itis preferred to use between 40'and 50 per cent of silicon, corresponding to a carbon range of approximately 0.1 to 0.04 per cent. Includedin this drawing are a number of points representing the silicon and carbon contents of low carbon ferrochrome-silicon and ferromanga'nese-silicon alloys in accordance with the present invention.

The prior direct reduction processes require carefuLcontrol at electric furnace temperatures, which makes operation diflicult, and the economics of the process causes the cost of the products to be considerably out of line in comparison with ferro-allo'ys of higher carbon content. This re.

sults, at least in part, in the high cost of stainless irons and steels.

Other ferro-alloys of carbide-forming elements appearto respond to the same general relationship just described. For instance, the commercial grades of ferromanganese-silicon alloys show the same general effect of silicon on the carbon content, as appears from the four following commercial grades:

Manganese Silicon Carbon Percent Percent Percent 1 Maximum. 2 Approximate.

A major object of the present invention is to carbide-forming elements, especially chromium and manganese, into lower carbon ferro-alloys .containing silicon for use as intermediate mate- I producing low carbon ferrous base alloys and also of lower silicon content than has heretofore been produced with such carbon contents.

Still another object is to provide low carbon ierro-alloys of the type referred to in which the carbon content is below that of alloys of the same silicon content produced by direct ore reduction, which are cheap, easily produced, and satisfactory for all purposes for which similar alloys produced by direct ore; reduction are used. These and other objects of my invention are attained in the manner now to be described.

The invention is predicated upon my discovery that, contrary to the belief expressed above, the carbon content of ferrochrome-silicon and similar ferro-alloys containing silicon is not directly or strictly dependent upon the silicon content, and that in simple and easy fashion these alloys maybe made with carbon contents below those to be expected for a given silicon content based upon the relationship previously accepted in the art and expressed in U. S. Patent No. 1,567,898. In accordance with the present invention this is accomplished by reacting a high carbon grade of the desired fcrro-alloy, ferrosilicon, and an oxidizing agent. In the practice of the invention the oxidizing agent serves primarily to oxidize the carbon and so lower its content to a point appreciably below that which would be expected for the silicon content of the product. The action of the oxidant is exothermic so that large amounts of heat are liberated, which desirably contributes to the economics of the process. In this manner there is produced a ferrosilicon alloy of the carbide-forming element present in the high carbon ferro-alloy which is of the low carbon content necessary for the production of such low carbon alloys asstainless irons and steels. and which may either contain less silicon than has been present in ferro-alloys of the same carbon grades, or less carbon for a given silicon content.

The invention may be practiced in various ways but to efiect reaction between the carbon oxidizing agent and the carbon it is necessary that at least the ferro-alloy or the ferrosilicon be molten. By way of example and not of limitation, the high carbon ferro-alloy, such as high carbon ferrochromium produced by direct ore reduction, may be mixed with the oxidizing agent and the mixture added to molten ferrosilicon. Alternatively, the ferrosilicon and the oxidizing agent may be mixed and added to molten high carbon ferrochrome or other ferro-alloy of a carbideforming element. Yet another possible pro-- cedure is to mix molten ferrosilicon and molten high carbon ferro-alloy in the presence of the oxidizing agent, or to add the oxidizing agent to a pre-formed mixture of the two. The high carbon ferro-alloy and the ferrosilicon'produce the desired ferro-alloy-silicon.

Various oxidizing agents capable of oxidizing carbon at a temperature at which one of the reactants is molten may be used such, for example, as nitrates, chlorates, perborates, persulfates, permanganates, and the like, especially those of the alkali metals, preference beingv given, of course, to the sodium'salts because they are more commonly available and usually cheaper than the ferro-alloy, and the car-bon content desired in the.

product. However, it may be stated that, generally speaking, the two ferro-alloys are mixed in proportions such as to give the desired content of silicon and alloying elementin the product, and the oxidizing agent is used in an amount such as to effect the desired reduction in carbon content. Also, as further guides to'the practice of the invention, it may be said that with ordinary high carbon ferro-alloys, such as those produced by direct ore reduction, it is advantageous to use ferro-silicon containing at least about 40 per cent of silicon. These two alloys should be proportioned so that the ferro-alloy-silicon product contains the desired amount of alloying element, in any event in excess of 5 per cent thereof, together with at least about 10 per cent of silicon. Desirably, the silicon will not exceed about 40 per cent in the finished ferro-alloy. The high carbon ferro-alloys used maybe those producedby direct ore reduction because they. may be made cheaply and easily. Such ferro-alloys may, of course, contain silicon due to the use of ores containing it, or to addition of silica to the furnace burden, which is desirable both because the presence of silicon lowers the melting point of the ferro-alloy, and also becaus the siliconcontaining ferro-alloys crush more easily.

For low carbon products the oxidant should be used in an amount such that the final alloy contains not over about 0.15 per cent of carbon, although much lower contents may be produced, as will appear hereinafter.

' The practicability of the invention in producing low carbon ferro-alloy-silicon alloys, particu larly those of substantially lower silicon content for a given carbon content than have been available heretofore, has been demonstrated by the extensive production of such alloys on a tonnage.

or commercial 'basis.- Examples from actual practice of ferrochrome-silicon alloys appear in the following table:

Silicon Chrome Carbon Alloy No.

Percent Perrenf Permit 1 n. 04 30. 5; 34. 78 2. 11.07 35. 88 16.15 3 0.06 37. 54 17. 90 4.. 0.12 33.14 20.60 5. 0. 04 36. 43 17.93 6. 0. 02 36. 16. 23 .7. 0. 05 31. 40 2'2. 75 8 0. 01' 38. 36 17. 33 9 0. 14 30. 11 26. in 0.06 31. 40 23.50 11 0. 11 27. 1O 29. l0 12 0.07 34. 93 18. 20

Alloy No. 1 was produced by ferrochrome containing 5.25 per cent of carbon and 69 per cent of chromium with per cent by weight of sodium nitrate and adding it to molten 78. per cent ferrosilicon. According to the carbon-silicon relationship described in Patent No.

trates clearly the profound effect of the oxidizingagent when used in accordance with this invention.

Alloy No. 2 was' made by adding high carbon ferrochromium and sodium. nitrateto molten 50 per cent ferrosilicon. According to .the graph of Patent No. 1,567,898 this alloy should have contained about 0.2 per cent of carbon. The other alloys were made in similar fashion, and it will be observed in each instance that the car'- bon content is below that which would have been expected.

Examples of ferromlanganese-sili'con alloys produced in accordancewith the invention are shown in the following table:

Alloy No. Carbon Silicon Manganese Percent Percent Percent These were made by adding mixtures of high carbon ferromanganese and oxidizing agent, such as sodium nitrate, to molten ferrosilicon.

The carbon and silicon contents of alloys Nos. 1 to 15 are representedby :cs in the accompanying drawing. It 'will be observed that in all of these alloys produced in accordance with the invention the carbon content for any given silicon contentis below that which would be expected according to existing belief in the art or produced by the direct reduction methods used heretofore.

These alloys may be used for the purposes and alloys containing the normal carbon content for a given silicon content. The term partially reduced ore as used herein has referenceto ore which has been subjected to reduction, by means of carbon or a reducing gas, to convert at least a portion, for instance more than ,2 per cent, of the metallic oxide to the metallic state.

The invention has been described with particular reference to the production of ferro-alloysilicons of very low carbon content. However. fromwhat has been said it will be understood that the gist of the invention resides in providing such alloys in which the carbon content for a given silicon content is less than that obtainable by direct reduction of ore and below that which would be expected according to prior art beliefs. Hence the carbon content, within the limitation just stated may be such as it requisite to the use to which the product is to be put, 1. e., it may be exceedingly low or relatively high but in all cases it lies below the graph shown inthe accompanying drawing. For instance, to make a ferrochrome-silicon for use in making stainless ferrous base alloys there may be used a ferrochrome produced by direci fireduction of ore to contain about per cent of silicon. According to the graph this will contain 2.5 per .cent of carbon. This is then reacted with ferroe silicon and oxidant to produce 'a ferro-chromesilicon with 40 to 50 per cent bf silicon and 0.01 to 0.02 per cent of carbon. In like fashion there mayl be made products containing less than 0.1 per cent of carbon at 4 0 per cent of silicon, less than 0.25 per cent of carbon at per cent of silicon, not over about 0.5 per cent of carbon .at 30 per cent of silicon, not'over 1.25 per cent of carbon at 25 per cent of silicon, etc., the carbon content in any given case lying below the curve shown in the drawing. a v

According to the provisions ofthe patent statutes, I have explained the principle and method of practicing my invention and have described what I now consider to represent its best embodiments. However, I desire to have it understood that, withinthe scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. That method of producing a low carbon ferro-alloy of silicon and a carbide-forming metal from a higher carbon 'ferro-alloy of said metal produced by direct reduction, ferrosilicon, and an oxidizing agent as reactants which comprises providing at least one of said ferro-alloys in molten condition and mixing therewith theother said reactants and by the reaction producing a ferro-alloy of substantially decreased carbon content.

2. That method of producing a low carbon ferro-alloy of silicon and a carbide-forming metal from a higher carbon ferro-alloymf said metal produced by direct reduction, ferrosilicon, and an alkali metal nitrate as reactants which comprises providing at least one of said ferroalloys inmolten condition and mixing therewith the other said reactants and by the reaction producing a ferro-alloy of substantially decreased carbon content.

3. A method of producing a low carbon ferroalloy of silicon and a carbide-forming metal according to claim 1 in which said ferrosilicon contains more than about 40 per cent of silicon, and said oxidant is sodium nitrate.

4. A method according to claim 1; in which saidcarbide-forming metal is of the group consisting of chromium and manganese and said ferrosilicon contains more than about 40 per cent of silicon.

5. That method of producing a low carbon ferro-alioy of silicon and a carbide-forming metal from a higher carbon ferro-alloy of said metal produced by direct reduction, ferrosilicon containing at least about 40 percent of silicon, and an oxidizing agent as' reactants,whi chcomprises providing at least one of said ferro-alloys in molten condition and mixing therewith the other said reactants and thereby producing said low carbon ferro-alloy, the amount of said agent being such that the ferro-alloy product-contains carbonin an amount less for a given silicon content than is producible' in the same alloy made by direct reduction.

6. Thatmethod of producing a low carbon ferro-alloy according to claim 5,- said carbideforming metal being of the group consisting of chromium and manganese, said ierrosilicon containing at least about 40 per cent of silicon, and said oxidizing agent being an alkali metal nitrate and being used in an amount such that the ferro-alloy product contains not over about 0.25 per cent of carbon.

7. That method of producing a low carbon ferro-alloy of silicon and a carbide-forming metal from a higher carbon ferro-alloy of said metal produced by direct reduction, from ferrosilicon and an oxidizing agent as reactants which comprises providing at least one of said ferroalloys in the molten state and then adding the other said reactants and thereby by reaction producing said low carbon ferro-alloy, said materials being so proportioned that the ferro-alloy product contains more than about 5 per cent of said carbide-forming metal, at least about per cent of silicon, the remainder being chiefly iron, and carbon in an amount which for the silicon present is less than contained in the same alloy produced by direct reduction.

8. That method of producing a low carbon ferrochrome-silicon from high carbon ferrochrome produced by direct reduction, ferrosilicon, and a carbon oxidant as reactants which comprises providing at least One of said ferroalloys in molten condition and mixing therewith the other said reactants and by reaction producing low carbon ferrochrome silicon alloy.

9. That method of producing a low carbon ferromanganese siliconfrom high carbon ferromanganese produced by direct reduction, ferrosilicon, and an oxidizing agent as reactants which comprises providing at least one of said ferroalloys in molten condition and mixing the other reactants therewith and by reaction thereof producing said low carbon ferro-alloy.

10. A method according to claim 2, said ferrosilicon containing at least about per cent of silicon.

11. A method according to claim 2, said nitrate being sodium nitrate.

12. A method according to claim 7, said agent being an alkali metal nitrate.

13. A method according to claim 7, said ferrosilicon containing at least about 40 per cent of silicon.

14. A method according to claim 7, said ferrosilicon containing at least about 40 per cent of silicon, said ferro-alloy being selected from the group consisting'of ferrochrome and ferromanganese, and said agent being sodium nitrate.

' JAMES C. VIGNOS. 

